<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #content { 
            height: 100px;
            width: 300px;
            border:solid 1px red;
        }
    </style>
</head>
<body>
    <button>点击请求数据</button>
    <div id="content"></div>

    <script>
        const btn = document.getElementsByTagName('button')[0];
        const box = document.getElementById("content");
        btn.addEventListener('click',function(){
            const xhr = new XMLHttpRequest();
            xhr.open('GET','http://127.0.0.1:8085/delay');
            //超时设置2秒
            xhr.timeout = 2000;
            //超时回调
            xhr.ontimeout = function(){
                alert("请求超时，请稍后重试！")
            }
            //设置网络异常回调
            xhr.onerror = function(){
                alert("你的网络似乎出了一些问题！")
            }
            xhr.send();
            xhr.onreadystatechange = function(){
                if(xhr.readyState == 4){
                    if(xhr.status >=200 && xhr.status<300){
                        box.innerHTML = xhr.response;
                    }
                }
            }
        })
    </script>
</body>
</html>